1. Field of the Invention
The present invention relates to the microbiological industry, and specifically to a method for producing L-arginine. The method uses a bacterium of the Enterobacteriaceae family which has been modified to attenuate expression of one or several genes encoding an L-arginine transporter.
2. Description of the Related Art
Conventionally, L-amino acids are industrially produced by fermentation methods utilizing strains of microorganisms from natural sources, or mutants thereof. Typically, the microorganisms are modified to enhance production yields of target L-amino acids.
Many techniques to enhance L-amino acid production yields have been reported, including by transforming microorganisms with recombinant DNA (see, for example, U.S. Pat. No. 4,278,765). Other techniques for enhancing production yields include increasing the activities of enzymes involved in amino acid biosynthesis and/or desensitizing the target enzymes of the feedback inhibition caused by the produced L-amino acid (see, for example, WO 95/16042 or U.S. Pat. Nos. 4,346,170; 5,661,012 and 6,040,160).
Other ways to enhance L-amino acid production yields is to attenuate expression of a gene or several genes which are involved in the degradation of the target L-amino acid, genes which divert the precursors of the target L-amino acid from the L-amino acid biosynthetic pathway, genes involved in the redistribution of the carbon, nitrogen, and phosphate fluxes, and genes coding for toxins, etc.
A transport system dependent on a binding protein in Escherichia coli specific for L-arginine was characterized by genetic and biochemical means. The system is made up of five adjacent genes, artPIQMJ (“art” stands for arginine transport), which are organized in two transcriptional units (artPIQM and artJ). The artI and artJ gene products, ArtI and ArtJ, are periplasmic binding proteins with sequence similarity to binding proteins for polar, or basic amino acids. The artQ, artM, and artP products are similar to known transmembrane proteins and the ATPase of binding-protein-dependent carriers. The mature ArtI and ArtJ proteins are localized in the periplasm and lack a signal peptide of 19 amino acid residues. ArtI and ArtJ were isolated from overproducing strains. ArtJ specifically binds L-arginine with high affinity and overproduction of ArtJ stimulated L-arginine uptake by bacteria. The substrate for ArtI is not known, and isolated ArtI did not bind common amino acids, various basic uncommon amino acids, or amines. It was concluded that the artPIQM artJ genes encode a third arginine-uptake system in addition to the known argT hisJQMP system of Salmonella typhimurium and E. coli and the arginine (-ornithine) carrier (aps) of E. coli (Wissenbach U. et al., Mol Microbiol.; 17(4):675-86 (1995)).
But currently, there have been no reports of attenuating expression of a gene encoding an L-arginine transporter for production of L-arginine.